1. Field of the Invention
The invention falls within the technological field of optical measuring instruments or equipment.
More particularly it relates to portable equipment for spectral and field characterisation of the reflection or reflectance coefficients and the transmission or transmittance coefficient of the receiver tubes used in thermal solar parabolic trough technology. The equipment includes all the components necessary to perform such measurement, mechanical adjustment to the tube, emission and detection of signals, processing of signals, display of results on screen and memory storage unit.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Solar energy collection, in its aspect of thermal collection, is becoming ever more technologically and economically important for the domestic production of hot water, heating or cooling and for the production of electricity in solar thermal power plants.
These systems require a maximum absorption of solar energy and the least possible energy losses. To this end, in parabolic collectors, receivers are configured by two concentric tubes: a first outer glass tube inside which there is an inner absorber metal tube usually made of steel, existing between them vacuum conditions that reduce losses due to conduction and convection. The inner tube has a coating with great solar energy absorbing power and low emissivity characteristics to reduce energy losses by thermal radiation in the far infrared spectrum.
Consequently, both in the domestic context and in the production of electricity, selective absorber coatings play an essential role and their proper functioning largely conditions the performance of such systems. This makes it vitally important to have a suitable device and a field characterisation method of the optical properties of these coatings. In the case of electricity production installations, due to the large number of absorber tubes to be characterised, it is also desirable that measurements can be taken quickly and easily.
Given the optical characteristics of such tubes (maximum energy absorption and minimum energy loss), the equipment must be capable of accurately measuring extreme values of the coefficients of reflection and transmission (close to zero or to a unit), generally in unfavourable environmental conditions because, logically, the ambient light is almost always of a high intensity.
Since these reflection and transmission coefficients depend on the wavelength of light in which they are evaluated, it is essential to perform a spectral characterisation thereof. Equipment taking this type measurement is called a spectrophotometer.
A classic spectrophotometer uses a light source with a broad spectrum and a variable filtering element, such as a mobile diffraction network followed by a narrow slit, making it possible to sequentially select different wavelengths. This option allows varying the wavelength almost continuously, however it is a more complex and delicate system and with a low dynamic range of measurement, since the input light power achieved is very low.
U.S. Pat. No. 4,687,329 describes equipment that uses a wide spectrum source, in this case ultraviolet spectrum, and various filters in fixed positions for spectral measurement at a number of discrete points.
Other prior registrations relate to spectrophotometers which use a collection of sources of different wavelengths as the light source. In US2008/0144004 several light emitting diodes (LED) are simultaneously used to perform a transmission measurement for the detection of various analytes in blood. However, it is not a true spectral measurement, yet several simultaneous measurements at a few different wavelengths. In addition, there is no protection against ambient light and reflection and reference measurements are not possible.
Something similar happens in the invention disclosed in U.S. Pat. No. 4,286,327, wherein a sequential measurement at different wavelengths (in the infrared spectrum) is indeed performed, but in this case the LEDs used are identical and the spectral selection is conducted by means of fixed filters with a different central wavelength. Neither is there a mechanism for recovering the signal away from ambient light, nor the possibility of performing reflection or reference measurements.
None of the above equipment or other similar ones meet the requirements for the field measurement of absorbent tubes for solar collectors, either based on range, sensitivity and/or mechanical configuration.
WO 2011/104401 is especially noteworthy. The main differences between WO 2011/104401 and the invention are pointed out below.
1) The device claimed in WO 2011/104401 requires a different optical channel for each wavelength in which it is measured, both in reflection and in transmission, while the equipment of the invention requires a single optical channel and running within, a radiation comprising the wavelengths of interest for measurement.
2) WO 2011/104401 fails to include any alignment system to detect the non-concentricity of the inner and outer tube of the receiver.
3) WO 2011/104401 fails to present an integrated visual interface in the device itself and communicates with a computer via a wireless network.
4) WO 2011/104401 has no mechanical adjustment of the equipment to the receiver tube.
5) WO 2011/104401 has no data storage unit.
6) The equipment described in WO 2011/104401 performs spectral measurements based on a set of LEDs arranged in line located on the equipment along the receiver tube, so there is an optical channel for each LED implemented. Each optical measurement channel is formed by a LED, a reference detector and a measurement detector, making a high number of detectors used in the equipment, which increases the complexity of the equipment. This optical configuration of the equipment determines the size of the equipment depending on the number of LEDs, the greater the number of LEDs, the larger the size of the equipment.
7) Both the system of WO 2011/104401 and that of the invention are affected by temperature variations, since the intensity of the radiation emitted by a LED, and shape of the beam, may vary with temperature. However, this unwanted interference of temperature in the operation of the WO 2011/104401 system, cannot be compensated or corrected because the detection and reference system is not configured to detect measurement alterations caused by temperature.
This is because in the system of WO 2011/104401 the reference detector does not receive all the light emitted by the LED, since the reference detector is located next to the LED and does not detect the entire surface of the LED (it has a biased view of it) and therefore neither does it detect the full beam of radiation emitted by it.
For this reason, the device of WO 2011/104401 does not ensure measuring the same light radiated in reference as in measurement, while the reflectivity and transmissivity measurement is less reliable than that of the device of the invention, due to possible variations in the beam due to temperature not detected by the reference detector.
8) In addition the system of WO 2011/104401 has no uniformity of the measurement beams because it directly uses the radiation from the LEDs. For this reason, the system has no sensitivity to changes in position of the tubes, i.e. the system has what is referred to in the description as a lack of geometric tolerance.
9) The present invention can comprise integrating spheres, which, in addition to optimising the space and the number of components used, allows to homogenise the light beam emitted, thereby improving signal quality.
The invention solves the problems described above by lightweight portable equipment that is fully autonomous, mechanically adjustable to the tube, which enables rapid execution and processing of measurements, and with suitable sensitivity and accuracy.